TLDR;
Mysql can't restart because it's out of memory, check that you have an appropriate swapfile configured.
Didn't help? If that's not your issue, more qualified questions to continue research are:
Background
I had exactly this problem on the very first system I set up on EC2, characterised by the wordpress site hosted there going down on occasion with "Error establishing database connection".
The logs showed the same error that the OP posted. My reading of the error (timestamps removed) is:
- Out of memory error:
InnoDB: Fatal error: cannot allocate memory for the buffer pool
- InnoDB can't start without enough memory
[ERROR] Plugin 'InnoDB' init function returned error.
[ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
[ERROR] Unknown/unsupported storage engine: InnoDB
[ERROR] Aborting
- mysqld is shutting down, which in this context, really means failing to restart!
[Note] /usr/sbin/mysqld: Shutdown complete
Checking /var/log/syslog and searching for mysql yields:
Out of memory: Kill process 15452 (mysqld) score 93 or sacrifice child
Killed process 15452 (mysqld) total-vm:888672kB, anon-rss:56252kB, file-rss:0kB
init: mysql main process (15452) killed by KILL signal
init: mysql main process ended, respawning
type=1400 audit(1443812767.391:30): apparmor="STATUS" operation="profile_replace" name="/usr/sbin/mysqld" pid=21984 comm="apparmor_parser"
init: mysql main process (21996) terminated with status 1
init: mysql main process ended, respawning
init: mysql post-start process (21997) terminated with status 1
<repeated>
Note: you may have to gunzip and search through archived logs if the error occurred before the logs were rotated by cron.
Solution
In my case the underlying issue was that I'd neglected to configure a swapfile.
You can check to see if you have one configured by running free -m.
total used free shared buffers cached
Mem: 604340 587364 16976 0 29260 72280
-/+ buffers/cache: 485824 118516
Swap: 0 0 0
In the example above, Swap: 0 indicates no swapfile.
Tutorials on setting one up:
Note that bigger is not necessarily better! From the Ubuntu guide:
The "diminishing returns" means that if you need more swap space than twice your RAM size, you'd better add more RAM as Hard Disk Drive (HDD) access is about 103 slower then RAM access, so something that would take 1 second, suddenly takes more then 15 minutes! And still more then a minute on a fast Solid State Drive (SSD)...
Regarding the other answers here...
The InnoDB memory heap is disabled
This isn’t really an error, just an indication that InnoDB is using the system’s internal memory allocator instead of its own. The default is yes/1, and is acceptable for production.
According to the docs, this command is deprecated, and will be removed in MySQL versions above 5.6 (and I assume MariaDB):
http://dev.mysql.com/doc/refman/5.6/en/innodb-performance-use_sys_malloc.html
Thanks to: Ruben Schade comment
[Note] Plugin 'FEDERATED' is disabled.
The message about FEDERATED disabled is not an error. It just meant that the FEDERATED engine its not ON for your mysql server. It's not used by default. If you don't need it, don't care about this message.
See: https://stackoverflow.com/a/16470822/2586761
